We investigate the influence of scattering processes in the continuum on the formation of lines in static, one dimensional atmosphere. It is shown that the Schuster mechanism of emission line formation can work under certain physical conditions. We derive formulae for the calculation of the line profiles in atmospheres with an ad hoc temperature

This paper combines data from the three preceding papers in order to analyze the multi-wave-band variability and spectral energy distribution of the Seyfert I galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and

We present the results of an intensive ultraviolet monitoring campaign on the Seyfert I galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously With the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra

In this Letter, we discuss a method to conduct a quantitative study of the star formation history (SFH) of Local Group (LG) galaxies using Hubble Space Telescope (HST) data. This method has proved to be successful in the analysis of the SFH of the same kind of galaxies using ground-based observations. It is based on the comparison of observed CMDs

We have obtained for the first time 2.10-2.45 μm infrared spectra of the soft-X-ray transient V404 Cygni. We determine a 95 per cent confidence upper limit to the fraction of light arising from the accretion disc of 14 per cent. The effect this has on the mass of the compact object, determined from modelling the infrared ellipsoidal variations, is

We argue that heights of formation (HOFs) should not be assigned to spectral lines since a single line my sample very different layers of the atmosphere, depending on the physical parameter of interest and the technique employed to determine it. HOFs should be assigned to specific measurements. General expressions to compute these HOFs for